This is only a good idea if you have vanilla Sins, and I don't think the AI uses novaliths in those. Novaliths can be easily counter by getting the auxiliary government upgrade on your starbases. They'll still leave a dent in your credit income but you won't have to recolonize and reupgrade the planets. And as the TEC on a large map credits should not be much of a problem.

Build a starbase on all your planets you care about and get the Auxilary Government upgrade, and think about sending in a raiding force of Ogrovs/Hoshiko/flak (hold position) to harass the enemy shooting Novalith warheads at you.

As for your main battle fleet, if you're still having problems rolling the Easy AI in a reasonable amount of time, just spam bombers along with a bit of flak... the AI has no idea how to deal with large numbers of enemy bomber squadrons.

I was curious, is there much turtling in this game to build up for an ultimate weapon, such as the Novalith? 

For example, Rush to a choke point planet next to their home star system (or close to it anyways) and then build up a fleet there and force him to attack you when you are strongest. In then mean time, you can work on the planets you skipped and colonizing them.

Then from there the turtling strategy would be to setup your novaliths and lob them at the enemy while you continue to build your fleet. I understand that Auxilary Government would mean that he wouldn't lose the planet, but there would be income loss correct? And when your fleet is sufficiently ready, go in and wipe him out?

Novaliths and super weapons in general are rarely used in ICO since games rarely get that long to even field them and frankly they really arn't worth the cost. But if it does than the only situation where it is probably "acceptable" to build one would be in the eco slot since you have no worries of the emeny jumping in on yah as soon as you attempt to build one.

Turtling works well against AI. Actually almost anything works well against AI since for defense they just throw themselves againsts the SBs.

Not really; the problem is that turtling tends to result in your economy being smaller than the enemy's, so they will probably reach superweapons first if you do this.

The most deadly way to use Novaliths on large scenarios is actually to spend everything on economy and rely on allies for defense.  Build up to a safe income (say 150 credits per second) and then start spamming novaliths.  Once you have 4-6 novaliths to shell enemy planets, switch your production to light carriers with bombers to go for the kill (either that or just send your income to an ally).

Yes; the problem is that while you are spending money on defenses and superweapons, he's spending it on military power.  Unless you thoroughly outplayed him in the early portion of the game and have your opponent boxed in with few options (he should just surrender at this point, and conventional military victory would easy anyways) he will be ready to attack you before you're ready to attack him.

I suppose I didn't quite make clear what I meant by "turtling". It's not true turtling in the sense you build up defenses around your planet and sit there. I would call it more aggressive turtling, in that you push out and colonize a planet close to their home system, preferrably at a choke point system and then backfill the other colonies while building that planet, as your fortress world. And I wasn't talking about rushing Novalith, but more building an nice big white picket fence and throwing nuclear goodness accross space. Anyways, I suppose that idea has been busted pretty well.

On the other hand, I was curious how aggressive player should be throughout the game. I understand that in the beginning, being aggressive with colonization can certainly pay dividends in the mid and late game. But does the average MP match come down to whoever get's the best position (i.e. a choke point world where he builds a fleet and a starbase to dare his opponent to come) and the other player trying to find a way to counter that position or at least spread out his fleet through the use of raids that weaken the fortress planet?